Optimization Design And Research Of Refrigeration System For The50m Light-purse Seine Vessel

The refrigeration systems consume lots of energy. The study on their energy saving would bein favor of the energy conservation and emission reduction, as well as economic benefit. Thisstudy focuses on the50-meter light purse seiner in the Shenhu fishing port in Jinjiang, FujianProvince, China. Through the calculation and comparison of data collected from the fieldinvestigation, the refrigeration system of the vessel is optimized with the results as follows.(1) The heat insulation layer of the low-temperature compartment in the fishing vessel isoptimized. The thickness of heat insulation layers of various types of cryogenic tanks in thefishing vessel are calculated and compared under three density of heat flow (7,9,11W/m2). Theresults show that the current heat insulation thickness200mm polyurethane (PU) foam is notenough for the freezing rooms when the density of heat flow is set as7W/m2, while there iscomparatively large waste for the cold seawater cabin. At the same time, with the heat flowdensity of9W/m2and11W/m2, all the three low-temperature cabins waste a lot in the heatinsulation layer. So in this type of fishing vessel, the current design of the heat insulation layer ofthe low-temperature cabins is not correct and needs to be improved.(2) The technical discussion and economic analysis are made on the application of vacuuminsulation panels(VIP) to the heat insulation layer of the freezing rooms (they have greattemperature difference between outside and inside). The results show that comparing the heatinsulation layer composed by VIP plus PU with the PU layer, the thickness of the former one willbe decreased by93mm than that of the latter. At the same time, the total capacity of the freezingroom in the vessel will increase by36.2m3for the former layer, and the initial investment costper unit heat transfer area will increase by57yuan for the former layer, which is acceptable. Thatis to say, it is economic and proper to apply the VIP to the heat insulation layer of the freezingroom in fishing vessels.(3) It is found that the existed compressors in the vessel are incapable of the cooling taskrequired by the refrigeration system based on the calculation by the author. Among them, it is tooslow for the compressor in cold seawater systems to cool the cold seawater cabin, and thecooling capacity of the compressor in freeze-refrigeration systems can’t satisfy the coolingrequirement for full load freezing rooms and refrigeration cabins. So the refrigerationcompressors in the fishing vessel should be re-matched. Two schemes of the compressor selection are proposed in this study. One is using pistoncompressor and the other is using screw compressor. These two options are compared andanalyzed from the perspective of the operating situation and performance under part load. Thesecond scheme is more suitable for the refrigeration system operated in the fishing vessels, witha better performance under part load and higher energy efficiency.(4) The condenser in the refrigeration system of the fishing vessel is also optimized, wherethere are four sets of condensers, with the total heat transfer area of260m2. According to thecalculation, the area of186m2will be enough for the current four compressors to worksimultaneously. There is a great waste for the existing condenser configuration.(5) Based on the cooling equipment load in every cold room, the heat transfer areas ofevaporators in the low-temperature cabins are calculated. Among them, the area in a freezingroom should be107.6m2and the length is900m for38steel pipes; while the area in arefrigerated compartment should be81.8m2and the length is685m for38steel pipes.Meanwhile, the evaporator area in the cold seawater cabin is determined by cooling time τ to thecold sea water, which is depended on the configuration of refrigeration compressors for coldseawater system.(6) The current refrigerant R22in fishing vessels belongs to the HCFC refrigerant, which isharmful to the atmospheric ozone layer. It can be used only during the transition period, andsome alternative green refrigerants should be found as soon as possible.Both the R290and R32are good substitute to the R22. However, the disadvantage of the R290is its flammability; and the re-design and match of the compressor and related components arenecessary as replacing the R22with R32, due to the difference in the system pressure andlubricants.